Sometimes it is necessary to save binary data such as zip
files, pictures or office documents into the database. Even if these files
are extracted from the database it is sometimes better to store the document
rather than recreate it through another query to the database. Also there
may be a need to archive an exact replica of a document that a customer
has received.
In this example we first compress all the .html and .csv files that
have been delievered to a customer. A zip file of all the reporting documents
is thus created. Then we insert the zip file into the SQL Server database
along with the customer number and week number. It is then saved and we
are free to overwrite any of the existing reports.
The field that holds the zip file has an image datatype. One might think
that the image datatype is just for graphic files such .jpeg, .gif
or .bmp and the datatype to use would be varbinary or binary. The naming
of the datatypes is misleading. In SQL Server 6.5 the binary and varbinary
can only hold 255 bytes. In SQL Server 7.0 the binary and varbinary have
a maximum storage of 8000 bytes. So image is the datatype to use for file
storage.
I chose to use Java for this task because it has excellent file IO and
database interfaces. It has a subclass specifically designed for file compression(to
create zip files). The Java database API, JDBC has specific methods for
writing and reading any kind of data to database.
Please note that this example uses a WebLogic JDBC driver. If you are
using a different driver you will need to change the way the connection
to the database is initiated.
The main tasks are to:
1) create a stream to hold the file for writing to the database (FileInputStream)
and use the setBinaryStream() to write to the database.
2) to fill a byte array with bytes from the database using the resultset’s
getBytes() method and to write to file system using a FileOutputStream.
Here are the most important methods of the FileDBTransfer class:
void insertZipFile(FileDBTransfer fdb, Connection cn, int CompID, int
WeekNum, String FileName)throws IOException, FileNotFoundException, SQLException
{
//variables
int FileLength;
FileInputStream fis;
String Query;
PreparedStatement pstmt;
//prepare FileInputStream
fis = fdb.getFileInputStream(FileName);
FileLength= fdb.getFileLength(FileName);
//Build the insert statement
//Create a parameterized query
Query = (“insert ReportArchive VALUES(?,?,?)”);
pstmt = cn.prepareStatement(Query);
pstmt.setInt(1, CompID);
pstmt.setInt(2, WeekNum);
pstmt.setBinaryStream(3, fis, FileLength); //method to insert
a stream of bytes
//execute the insert statement
pstmt.executeUpdate();
}// end insertZipFile
Reading from the database is even simpler:
void getBinaryFile(String FileName,ResultSet rs) throws IOException,
FileNotFoundException, SQLException
{
//Array to hold array of file bytes
byte[] fileBytes; //an array of bytes
if (rs.next()) //if there is a record
{
fileBytes = rs.getBytes(1); //create a byte array from contents
of field
OutputStream targetFile= new FileOutputStream(FileName);
// define the output stream
targetFile.write(fileBytes); //write the array of bytes to file
targetFile.close(); //close the File stream
}
}
The files used are:
1) FileDBTransfer.java This is the class that contains
methods for reading and writing files to the database. It cannot be executed
directly, but rather must be instantiated and used in other classes.
2) saveToDB.java Instantiates the FileDBTransfer class
and executes methods to upload a file to database
Structure: java saveToDB [CompanyID] [Week] [FileToUpload]
Call:java saveToDB 10 32 “out.zip”
3) saveToFile.java Instantiates the FileDBTransfer
class and executes methods to download a file from database
Structure: java saveToDB [CompanyID] [Week] [TargetFile]
Call:java saveToFile 10 32 “out2.zip”
4)archiveReports.java Class to zip up files. This class has a
main method inside it and thus instantiates itself, but it may also be
instantiated by other classes,
Call: java archiveReports d:mydir
5)OnlyExt.java
This is a class used by archiveReports.java program to filter a listing
of files from a directory.
6) ReportArchiveTable.sql
An example table that contains an image datatype and is used in this
article.
7)Javadoc.zip
Documentation files generated by javadoc
